- 01Low with sodium means diluted; low on its own means lost
If sodium and chloride fall together, the body is holding extra water. If chloride falls and sodium stays normal while bicarbonate rises, chloride has been lost through vomiting or the kidneys. Sodium minus chloride, normally in the 30s, shows which.
Chloride is low under about 98 mmol/L, and on its own it rarely means much. Doctors read it next to two neighbors on the same report, sodium and bicarbonate (often printed as CO2), and the pattern of the three shows whether chloride has been diluted by extra water or lost from the stomach or the kidneys. Hypochloremia, the medical word for low chloride, is seen more often in people who are unwell or in hospital; in healthy adults having routine bloods, one value a point or two under the line usually earns a repeat test and nothing more.
Read low chloride beside these
How low is low chloride (hypochloremia)? The numbers on your report
Chloride is part of the routine basic and comprehensive metabolic panel, taken from a standard blood draw with no special preparation. The usual adult reference range for serum chloride is about 98 to 106 mmol/L 1. Ranges vary a little between labs, with some starting at 96 and some running the top to 107 or higher, so read your result against the range printed on your own report. Chloride carries a single negative charge, so a result in mEq/L and the same result in mmol/L are the same number 1; the lab units guide covers why.
Where an example chloride of 95 sitsmmol/L
| Chloride (mmol/L) | What it usually means | What happens next |
|---|---|---|
| 98 or above | Inside the usual range | Nothing for chloride; see chloride 98 |
| 96 to 97 | One or two points under the line, often lab variation or a passing shift | Repeat at your next routine test if sodium and bicarbonate are normal; see chloride 97 |
| 90 to 95 | Mildly low, often with a cause worth finding (fluids, stomach losses, medicines) | Doctor reviews sodium, bicarbonate, potassium and medicines; see chloride 95 |
| Under 90 | Markedly low, uncommon outside illness | Contact a doctor the same day |
Low sodium and low chloride, or chloride low on its own? The three patterns
Chloride is the main negatively charged ion in the fluid outside cells, making up about 70% of the body's negative ions, and it moves in step with sodium 2. That gives the one check that sorts most low chloride results: did chloride fall together with sodium, or did chloride fall further than sodium?
When sodium and chloride fall together, water is the usual story. The body is holding more water than salt, which dilutes both, as in drinking large volumes of plain water, SIADH (a hormone signal that makes the kidneys keep water), heart failure, cirrhosis, advanced kidney disease or thiazide diuretics 26. When chloride falls and sodium stays normal, chloride has been lost on its own, and bicarbonate rises to take its place 3.
| Sodium | Chloride | Bicarbonate (CO2) | Likely meaning |
|---|---|---|---|
| Low | Low | Normal | Dilution: too much water relative to salt (water overload, SIADH, heart, liver or kidney fluid overload, thiazides) |
| Normal | Low | High | Chloride loss with metabolic alkalosis: vomiting, nasogastric suction (a tube through the nose draining the stomach, used in hospital), loop or thiazide diuretics |
| Normal | Low | High, with known lung disease | The kidneys holding bicarbonate to offset carbon dioxide held in by the lungs, as in COPD |
| Normal | 96 to 97 | Normal | Usually lab variation; repeat |
The anion gap, which is sodium minus the sum of chloride and bicarbonate, uses the same three numbers, so a low chloride shifts it too. The anion gap page explains what the gap shows, and if yours comes out low, the low anion gap page explains why. Run your own numbers through the calculator below.
CalculatorAnion gap calculatorPuts your sodium, chloride and bicarbonate into one number doctors use to read acid-base balanceWork it out Low chloride and high CO2: what the pair means
Blood has to stay electrically balanced, so when the negatively charged chloride falls, another negative ion has to rise, and that ion is usually bicarbonate. Low chloride plus high bicarbonate (high CO2 on most reports) is the signature of metabolic alkalosis, where the blood has tipped slightly alkaline. Stomach juice is rich in hydrochloric acid, so vomiting or a stomach tube removes chloride and leaves bicarbonate behind 3. Loop and thiazide diuretics do the same through the urine, and they are among the most common causes of low chloride with high bicarbonate 3.
Low potassium often travels with this pattern, because the same losses and the same kidney response drain potassium, and it is the part most likely to cause symptoms. Doctors call it a chloride-depletion alkalosis because putting chloride back is what corrects it: the kidneys cannot release the extra bicarbonate until chloride is replaced, usually as saline and potassium chloride given under medical supervision 3. As the high CO2 page puts it, most high results "come from a diuretic, vomiting, or the kidneys holding bicarbonate to offset CO2 trapped by the lungs."
What causes low chloride
Most low chloride results on a routine panel trace back to vomiting, a diuretic or a low sodium; rarer causes usually show up because something else on the panel is off too.
| Group | Causes |
|---|---|
| Stomach and gut losses | Vomiting, nasogastric suction, laxative overuse, rare chloride-losing diarrhea (most diarrhea raises chloride instead) |
| Medicines | Loop diuretics such as furosemide and bumetanide, thiazides such as hydrochlorothiazide and chlorthalidone, heavy use of sodium bicarbonate or bicarbonate antacids |
| Dilution (sodium low too) | Heart failure, cirrhosis, advanced kidney disease, SIADH, drinking large volumes of plain water, including during long endurance events 6 |
| Hormones | Adrenal insufficiency (Addison's disease), where sodium falls and potassium is often high; chloride may fall less than sodium |
| Lungs | Long-term lung disease that holds in carbon dioxide, such as COPD (chronic respiratory acidosis), where the kidneys keep bicarbonate and pass out chloride 2 |
| Rare | Bartter and Gitelman syndromes (inherited kidney salt wasting, with low potassium and alkalosis) 3, cystic fibrosis with heavy sweat losses, mostly in children |
Symptoms of low chloride
A low chloride rarely causes symptoms by itself, and a mildly low chloride found on routine bloods usually comes with none. What people feel comes from the cause or from what travels with low chloride. Dehydration from vomiting brings thirst, dizziness on standing and dark urine. A low sodium brings headache, nausea and, when marked, confusion 6. Low potassium and alkalosis bring weakness, muscle cramps, tingling around the mouth or fingers and palpitations. Tiredness is common and nonspecific; the fatigue page covers the other tests that check it.
Does low chloride mean heart failure?
A low chloride in someone without heart disease does not point to heart failure; vomiting, diuretics and low sodium are far more likely. The link runs the other way: in people who already have heart failure, low chloride is a recognized warning sign. In a study of patients admitted to hospital because their heart failure had suddenly worsened (acute decompensated heart failure), low serum chloride on admission was independently linked to higher mortality, and more strongly than low sodium 4. Much of that low chloride is driven by diuretics, and in heart failure low chloride is linked with diuretic resistance, where the water pills stop working as well 5.
If you have heart failure and your chloride has dropped, raise it with the team that manages your diuretics, because it can change which diuretic they choose.
What your doctor checks next
- 1Repeat with a full electrolyte panelA single slightly low chloride with normal neighbors is often gone on a repeat test.
- 2Read the neighborsSodium, potassium, bicarbonate, anion gap and kidney function (creatinine and eGFR) sort the pattern.
- 3Review medicinesDiuretics, laxatives and antacids are the usual suspects; the doctor checks doses and recent changes.
- 4Urine chloride when the cause is unclearIn metabolic alkalosis, a urine chloride under about 20 to 25 mmol/L points to vomiting or past diuretic use; a higher value points to current diuretics, Bartter or Gitelman syndrome, or too much of the salt-retaining hormone aldosterone 3.
- 5Osmolality when sodium is low tooSerum and urine osmolality (how concentrated the blood and urine are) and urine sodium separate water overload, SIADH and adrenal causes 6. A blood gas is added when the acid-base picture is unclear.
Tests that usually come next
How low chloride is raised
Low chloride is corrected by treating the cause, and the fix depends on which pattern your results show. When vomiting or a stomach tube is draining chloride, stopping the loss and replacing fluid corrects it. When a diuretic is the cause, the prescriber may change the dose or the drug, and low potassium is replaced as potassium chloride, which also restores chloride 3. When someone is dry, saline restores both volume and chloride 3. When the cause is dilution, the approach is the opposite: limiting water, and treating the heart, liver, kidney or hormone problem behind it 6.
Dietary salt is rarely the problem in people with healthy kidneys, because a typical diet supplies far more chloride than the body needs. No supplement in the evidence base raises chloride in a useful way.
When a low chloride is urgent
Read your whole panel
A chloride result only makes sense next to sodium, potassium, bicarbonate and kidney function, which all sit on the same metabolic panel. The metabolic panel guide walks through that report line by line, and the electrolytes guide explains how the electrolytes balance each other. If kidney function is part of the picture, the kidney function guide explains creatinine and eGFR, and a single low reading is best judged against the next one (why trends beat single readings).
Free, no accountRead your blood testRead a metabolic panel with a low chloride alongside your sodium, bicarbonate and potassium, line by line.Read my results
Citations
- Morrison G. Serum Chloride. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations, 3rd edition. Butterworths, 1990.
- Berend K, van Hulsteijn LH, Gans RO. Chloride: the queen of electrolytes? Eur J Intern Med, 2012.
- Do C, Vasquez PC, Soleimani M. Metabolic Alkalosis Pathogenesis, Diagnosis, and Treatment: Core Curriculum 2022. Am J Kidney Dis, 2022.
- Grodin JL et al. Prognostic role of serum chloride levels in acute decompensated heart failure. J Am Coll Cardiol, 2015.
- Zandijk AJL et al. Chloride in Heart Failure: The Neglected Electrolyte. JACC Heart Fail, 2021.
- Spasovski G et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol, 2014.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
